I agree with everyone here, check the search button, but I'll save you the hassle.The s13 primarily came with the red top sr20det, and the 180sx came with a black top, of those they are identical, same stuff, which is why sometimed you might find a black top for just a little bit more.The s14 came with black tops only, and these engines are what most people would argue the ones to get. It comes with a ball bearing turbo and VTC so the turbo can withstand more boost than the red top and has VTC (think watered down VTEC which is for you to decide whether or not you like it.Also, another reason why the black tops are more expensive is because they're newer motors, so you know how that goes. Hope that helps, if you really want it broken down, go to
http://www.heavythrottle.combut yeah man, search in the future, people love to flame about that kind of stuff, this stuff is really easy to find.